Laminates are well known in the art, particularly for use as prefabricated building panels. Composite panels, such as those disclosed in U.S. Pat. No. 3,331,174, provide light weight economical structures, wherein a stiff foam core fills the area between two parallel fiber reinforced plastic sheets spaced apart by spacing members. The foam is adhered to the inner surface of each plastic sheet as well as to each spacing member. However, such spacing members contribute to the weight of these prior art composite panels. Conventional materials used in prefabricated structures, such as wood, plywood, particle board or oriented strand board, as well as laminates such as those mentioned above, while providing sufficient levels of strength and economy, generally exhibit a low level of fire resistance.
Light weight, high strength fire resistant structures having a compressed fiber reinforced thermoplastic layer covering a foam or wooden substrate are known in the art. When exposed to temperatures normally experienced in a fire, the fiber reinforced thermoplastic layer expands or "lofts" to twice its original thickness, thus creating a fire barrier protecting the substrate. Although these lofted thermoplastic materials combine stiffness and strength with both light weight and high fire resistance, the surfaces of the lofted thermoplastic structures are porous. The porous nature of such materials is disadvantageous for use as building panels because it permits water absorption; it provides a poor surface for repainting; and it results in poor insulating properties.